Homeowner treating algae in an irrigation pond.by Bill and Mary Weaver
Farm ponds can be both beautiful and functional as irrigation reservoirs. In addition, having a pond can save you about 10 percent on your farm insurance premium, if you install the right type of fire hydrant hookup for your local fire department. “These hook ups cost only a couple hundred dollars to put in,” commented Bryan Swistock, Penn State Water Resources Extension Coordinator. Some regular attention to potential problems can help to keep your pond from causing you headaches. Here are some suggestions from Swistock for irrigation pond owners, starting with ones that could be less obvious until you find yourself clobbered by them.

Unwary growers can be hit out of the blue with clogged irrigation equipment and blackened crop leaves because of a potential problem, particularly in deeper ponds, that is surprisingly easy to solve. Often in mid-summer, the deeper water layers become anoxic. In the absence of oxygen, high levels of manganese, iron and other dissolved metals can mobilize out of the sediment at the bottom of the pond and enter your irrigation water, oxidizing on and blackening plant leaves and clogging pipes and tubing. To solve this common problem before it occurs, simply raise the intake for your irrigation water above the anoxic deeper level, where it won’t pick up water with the high concentration of dissolved metal. You could suspend the intake, or just set up your irrigation so you’re only removing water from the top of the pond. According to Swistock, “You could also solve this problem by installing aeration in your pond to prevent anoxic conditions from forming.”
Irrigation ponds are commonly built with fairly steep sides. The idea is to hold a lot of water. But if the sides of the pond are too steep, you can get slumping of the upper bank. The topsoil just sloughs off, and walking near the pond can become dangerous. “We usually recommend building at least a two-to-one slope, to prevent slumping,” explained Swistock. “That will still give you a pond that will hold a lot of water. If you see slumping, use common sense. Keep foot traffic away from the edges of the pond. Stabilize banks to prevent erosion, and control Canada geese.
Determine, before you apply chemicals to treat for algae or other nuisance plants, exactly how many acre-feet of water your pond contains. There are roughly 325,000 gallons per acre-foot of pond. Calculating water-holding capacity is easier than it has ever been, thanks to the help of computers and cell phones with GPS. Why is this precision so important? Many ponds, irrigation and otherwise, have problems with algae and submerged or floating plants. If you assume your pond is larger than it is, and dump the amount of herbicide in the pond for the size you assume it is, the result could be a fish kill – in your pond, or in a stream that flows through it. “Also, before you apply herbicide to your pond, be sure to identify the specific plants that are causing the problem,” advised Swistock. You have back-up help available for this. “If you can take a good digital photo and email it to me, I’ll tell you what it is so you can determine the correct chemical to use.”
Know the “residence time” of the water in your pond. Why? The residence time is how long the water in your pond has been there, on average. Some herbicides for algae and other water plants need 20, 30 or even 60 days of contact time to be effective. Make sure the chemical will be in your pond long enough to do the job before you buy it.
Cut down on the amount of run-off nutrients, particularly nitrogen and phosphorus that are reaching your pond water. This will help to minimize problems with algae and nuisance water plants. If your pond’s drainage area contains a lot of fertilized crop fields, plant buffer strips, plants that will take up and use at least a portion of those nutrients before they reach the pond. Be sure to maintain septic systems. Keep sediment from reaching the pond. Sediment makes the pond shallower, allowing more light to reach the depths, which encourages more algae and plant growth in the presence of nitrogen and phosphorus.
In addition to herbicides, on which regulations can differ from state to state, there are some other strategies you can use to control algae and nuisance water plants in ponds. “Herbicides can be very effective,” commented Swistock, “but can also be expensive in some cases. For example, you could introduce grass carp into your pond to eat some of these plants. Aerating the water could also be used to cut down on the growth of algae. Or you could simply pull or manually remove the plants.
Canada geese can be a real headache in an irrigation pond, both because they could be source of E. coli, and their droppings will be a source of nutrients, encouraging algae and water plant growth. According to Swistock, Canada geese are another problem that can have a rather simple solution. “Geese like manicured lawn right up to the edge of the pond,” explained Swistock. “If you don’t cut the grass and weeds around the edge of the pond, they’re likely to leave and head for the golf course. Geese get nervous about predators in even a little high grass, so that can be an easy control strategy.
To check water quality, with an irrigation pond, it is wise to take at least one sample a year to check for nutrients that could impact irrigation. “I’d suggest checking pH, and certainly metals like manganese and iron. E. coli, more of a problem in runoff ponds, should be included for GAP testing. Also include nitrates and hardness levels, especially if you’re thinking about using copper-based herbicides for algae control. “Penn State tests pond and lake water. In a recent survey, 12 percent of ponds had high E. coli levels. If you only take one sample, take it at the outlet of the pond,” advised Swistock. “Ideally it’s best to take several samples, at a variety of depths.”
An annual pond inspection can spot potential problems before they become serious. Look for early signs of leaks, such as wet areas on the outside of the dam. “If small trees or woody vegetation is starting to grow on the dam, remove it, but leave large trees alone,” he advised. Make sure you have an effective trash rack over the top of your overflow pipe. Clogs are easier to prevent than to clean out. Look for signs of unfamiliar plants that may be invasive. Muskrat holes can cause pond leaks. The solution is to rip rap the inside of the pond with rocks so the muskrats can’t dig there.
If you’re thinking of constructing a pond, be aware that most leak problems result from hiring contractors who were not experienced in building ponds. “Our pond website has a wealth of information about all aspects of building farm ponds,” continued Swistock. “If you study it carefully, you could prevent a lot of future headaches.”